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Discussion Starter #1
Got my car protuned about a month ago. Immediately ran into issues going above 17psi (started getting knock).
Its been a mystery as to what was causing it. Gone through many things, bad gas being the only thing that cant be checked.

I decided to do a compression test to see if i have ringland issues or washed cylinders (previous tune was a very rich opensource).

The numbers are a bit low, but consistent (warm motor).

Cylinder:
1. 135
2. 138
3. 135
4. 138

Any one have any input if this is too low or possibly the cause of my knocking at high boost.


PS - the car has 80,000km
 

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Actually since the four are in the same range i wouldn't bother about the numbers high or low.
1. When was the performed when the car was warm?
2. Every apparatus is different some compression guages reads less than others.
3. How is the test is performed?
 

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My 184,000 mile motor did 140 warm.

My STI manual shows:

Compression (350 rpm and fully open throttle):
Standard
981 — 1,177 kPa (10 — 12 kgf/cm2, 142 —
171 psi)
Limit
882 kPa (9.0 kgf/cm2, 128 psi)
Difference between cylinders
Less than 49 kPa (0.5 kgf/cm2, 7 psi)

So still within the low limit.
 

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Discussion Starter #4
Actually since the four are in the same range i wouldn't bother about the numbers high or low.
1. When was the performed when the car was warm?
2. Every apparatus is different some compression guages reads less than others.
3. How is the test is performed?

The car was warm

The gauge was brand new, but thats understandable

followed an IWSTI DIY. coils out, plugs out, fuel pump fuse pulled. let the car crank approx. 6 times. Did this multiple times per cylinder and took the average for each.
 

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Discussion Starter #5
My 184,000 mile motor did 140 warm.

My STI manual shows:

Compression (350 rpm and fully open throttle):
Standard
981 — 1,177 kPa (10 — 12 kgf/cm2, 142 —
171 psi)
Limit
882 kPa (9.0 kgf/cm2, 128 psi)
Difference between cylinders
Less than 49 kPa (0.5 kgf/cm2, 7 psi)

So still within the low limit.

Its definitely in the low limit. Would these numbers effect power if i got the car tuned?

I also didn't hold the throttle wide open. Not sure if this would effect the numbers...
 

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As long as your numbers stay within 5-10psi roughly that is acceptable to stay in spec. The actual number is relative to a point. I say those are very good numbers for a street car. If you were building a race car and looking for highest compression in all cylinders then to the drawing board and going through the wallet would be due. Would require engine blueprinting. Go get it tuned. I had similar numbers prior to my tune making approx 350whp. I am an oil guy coming from old 911's so I would invest in oil temp and pressure gauges. It tells a lot about how the engine runs.
 

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I would question the tune for the knock. I don't want to say your tuner is jacked up but we are all human and make mistakes. Check the big three. Air intake fuel and spark. If you have a deficiency in one of those areas knock could cause knock
 

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does it matter if its tested cold or warm? i had mine tested cold and got 158-160 for all cylinders and tested it twice to make sure after doing a full round on each cylinder
 

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what is important is how quickly the cylinder pumps up to the max compression reading on the gauge.....it should reach the max read within 3 or 4 at the most revolutions....if it reaches say 150PSI but takes 10 revolutions of the piston to TDC on the compression stroke it's loosing compression and a leakdown test should be performed next to pinpoint the problem.
 

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what is important is how quickly the cylinder pumps up to the max compression reading on the gauge.....it should reach the max read within 3 or 4 at the most revolutions....if it reaches say 150PSI but takes 10 revolutions of the piston to TDC on the compression stroke it's loosing compression and a leakdown test should be performed next to pinpoint the problem. So on engines where the average readings are on the lower side, that can be an important clue when doing the test.
 
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